1. Field of the Invention
The present invention relates to an optoelectronic arrangement and a method for operating the same, in particular a specific control arrangement for one or more light switches for optical signals guided in a light waveguide, applied on a first substrate, for example consisting of gallium arsenide or lithium niobate, and designed as a directional coupler having two light waveguides arranged in parallel and closely adjacent one another along a switching path which is capable of through-connecting or cross connecting.
2. Description of the Prior Art
The present invention was developed, in particular, for the control of a plurality of light switches which are manufactured on a single first substrate in integrated technology and, in particular, are to serve as crosspoints of a switching network having purely optical links in a telephone exchange system. However, in addition, the invention can also be employed in other technical fields of application, for example, for controlling light switches in computer technology and in other systems and apparatus transmitting or processing signals, primarily in case there must be individually supplied to each of the different light switches, for example brought about by manufacturing tolerances, a differently great electric control voltage of a precisely-adjusted amplitude.
Electrically-controllable light switches are per se constructed in various manners, primarily depending upon the type of through-connection required. In light switches constructed in the form of directional couplers, through voltage-dependent light velocity changes, the correspondingly co-changed cross couplings between two light transmissions, most frequently closely adjacent and extending parallel to one another, are utilized for direct or cross connection of both light transmissions. If the second parallel light transmission terminates in a light absorbing light sink, then the directional coupler cooperates like a light switch similar to the Kerr cell, viewed externally, with a single light transmission as a signal output. Moreover, there are, for example, similar to the direction of couplers, controllable light branch connections for the switching of the signals to the one or other branch connection output. Such light switches contain, respectively, one or more electrically-conducted electrodes for the control of the through connection.
Such light switches and their control arrangement, are already known and discussed in a plurality of references, whereby the light switches therein are preferably directional couplers, preferably manufactured on a GaAs base or a LiNbO.sub.3 base in integrated technology, and whereby the control arrangement essentially is formed by a single frequently controllable DC voltage supply apparatus and controls a single light switch, respectively, cf. the light switches and their control arrangement in:
(1) Taylor H. F. "Optical Waveguide Connecting Networks", Electronics Letters, Vol. 10, No. 4, Feb. 21, 1974, pp. 41-43;
(2) Sasaki et al "Electro-optic Y-Junction Modulator/Switch", Electronics Letters, Vol. 12, No. 18, Sept. 2, 1977, pp. 459-460;
(3) Schmidt et al, "Experimental 4.times.4 Optical Switching Network", Electronics Letters, Vol. 12, No. 22, Oct. 28, 1976, pp. 575-577;
(4) Schmidt et al, "Metal-diffused Optical Waveguides in LiNbO.sub.3 ", Applied Physics Letters, Vol. 25, No. 8, Oct. 15, 1974, pp. 458-460;
(5) Tada et al, "A New Light Modulator Using Perturbation of Synchronism Between Two Coupled Guides", Applied Physics Letters, Vol. 25, No. 10, Nov. 15, 1974, pp. 561-562;
(6) Campbell et al, "GaAs electro-optic directional-coupler switch", Applied Physics Letters, Vol. 27, No. 4, Aug. 15, 1975, pp. 202-205;
(7) Papuchon et al, "Electrically switched optical directional coupler: Cobra", Applied Physics Letters, Vol. 27, No. 5, Sept. 1, 1975, pp. 289-291;
(8) Schmidt et al, "Electro-optically switched coupler with stepped .DELTA..beta. reversal using Ti-diffused LiNbO.sub.3 waveguides", Applied Physics Letters, Vol. 28, No. 9, May 1, 1976, pp. 503-506;
(9) Papuchon et al "Electrically active optical bifurcation: BOA", Applied Physics Letters, Vol. 31, No. 4, Aug. 15, 1977, pp. 266-267;
(10) Kogelnik et al, "Switched Directional Couplers with Alternating .DELTA..beta., IEEE Journal of Quantum Electronics, Vol. QE-12, No. 7, July 1976, pp. 396-401; and
(11) Blum et al, "Monolithic GaAs Circuit Elements for Integrated Optics", Integrated Optics Conference, Salt Lake City, Utah, Jan. 12-14, 1976, pp. MA4-1 to MA4-3,
all of the above being fully incorporated herein by this reference.
A plurality of such light switches, applied on one, or on several substrates, respectively, can therefore serve as crosspoints of a switching network having purely optical links in a telephone exchange system, to which, in particular, in the above-cited publications (1) and (3), reference has been taken. Such light switches can, in an equivalent fashion, frequently replace 2.times.2 switches in switching networks for purely electrical signals instead of for optical signals, in particular, switches which per se are already known, for example through:
(12) U.S. Pat. No. 3,638,193;
(13) U.S. Pat. No. 3,593,295;
(14) German Offenlegungsschrift No. 1,922,891;
(15) German Auslegeschrift No. 2,036,128;
(16) German Auslegeschrift No. 2,036,176; and
(17) Joel Jr. "On Permulation Switching Networks", The Bell System Technical Journal, May-June 1968, pp. 813-822,
all of which are fully incorporated herein by this reference.
Essentially, this equivalency has already been pointed out in
(18) German Offenlegungsschrift No. 3,138,979; and
(19) German Offenlegungsschrift No. 3,138,980,
which were not published before the effective filing date of this document.
In addition, it is already known to control the above-mentioned light switches through control arrangements which contain transistors, or diodes, respectively, on the first substrate or on a second substrate, for example one may refer to:
(20) Schmidt et al "Efficient optical waveguide switch/amplitude modulator", Optics Letters, Vol. 2, No. 2, February 1978, pp. 45-47, particularly p. 45, left column, second paragraph;
(21) Goldberg et al "Silicon photodiode for optical channel waveguides", Applied Physics Letters, Vol. 37, No. 2, July 15, 1980, pp. 195-197;
(22) Carenco et al, "Monolithic Integration of a Detector and a Directional Coupler Switch in GaAs-Bistable Operation", 6th ECOC (European Conference on Optical Communication), Sept. 16-19, 1980, IEEE Publication No. 190, pp. 252-255, particularly p. 252, first paragraph and FIG. 3; and
(23) Wilt et al, "Low Threshold Be Implanted (GaAl) As Laser on Semi-Insulating Substrate", IEEE Journal of Quantum Electronics, Vol. QE-16, No. 4, April 1980, pp. 390-391,
fully incorporated herein by this reference.
It is also already known in the art to produce a first GaAs substrate with light transmission members on a SiO.sub.2 layer, for example one may refer to:
(24) Electronic Newsletter, "Guide Promises Low Losses for Optoelectronic ICs", Electronics, June 2, 1981, p. 33,
fully incorporated herein by this reference.
Such optoelectronic light switches have the often interfering disadvantage that the control voltage, or the control potentials of the control voltage, respectively, frequently must be very accurate, e.g., adjusted to 1.degree./oo(per mille) precisely in order to obtain an optimum operation. If, in particular, the control voltage is not sufficiently precisely adjusted, then either the crosstalk attenuation between various optical guides of the light switch, and possibly the entire first substrate, is unfavorable, or other attenuations within the light transmission members are unfavorable. Particularly for the utilization of such light switches as crosspoints of a telephone exchange system having purely optical links, however, extremely high requirements must be made of the crosstalk attenuation, on the one hand, and of the passband attenuation, on the other hand, of the light transmission member.
Due to the integrated manufacturing technique and the related relatively large manufacturing tolerances, in particular, for the light transmission members, however, the respectively accurate magnitude of the control voltage, necessary for the purpose of optimum control, is quite different from case-to-case. The truly optimum magnitude of the control potentials for each of the light switches on such a first substrate can only be ascertained from case-to-case through measurements whereby, in the latter operation, for each light switch of many light switches applied on the same first substrate, respectively varying great control potentials are favorable, i.e. optimum.